Aromatization Catalyst Preparation with Alkali Metal Present During a Washing Step

ABSTRACT

Methods for producing supported catalysts containing a transition metal and a bound zeolite base are disclosed. These methods employ a step of washing the bound zeolite base in the presence of an alkali metal, prior to impregnating the bound zeolitic support with the transition metal. Alkali metals such as potassium and cesium may be used.

FIELD OF THE INVENTION

The present disclosure concerns methods for producing supportedcatalysts, and more particularly relates to the production of supportedaromatization catalysts containing a transition metal and a boundzeolite base using a washing step in which an alkali metal is present.

BACKGROUND OF THE INVENTION

The standard manufacturing process for many supported aromatizationcatalysts typically involves forming a bound zeolite base from a binderand a zeolite, and the zeolite may be ion-exchanged prior to formationof the bound zeolite base. The bound zeolite generally is washed priorto the addition of a transition metal, such as platinum, and a halogen,thereby forming the supported aromatization catalyst.

It may not be desirable to perform an ion-exchange process after theformation of the bound zeolite base, due in part to the additional costand complexity that it would add to the overall manufacturing process ofthe catalyst. However, it may be beneficial to enrich the bound zeolitesupport with an alkali metal to improve the properties of the resultantsupported aromatization catalyst without the necessity of anion-exchange process. Accordingly, it is to these ends that the presentdisclosure is generally directed.

SUMMARY OF THE INVENTION

Methods for producing supported catalysts are disclosed and describedherein. One such method for producing a supported catalyst may comprise(a) providing a bound zeolite base, (b) washing the bound zeolite basewith an aqueous solution comprising an alkali metal to produce an alkalimetal enriched zeolite support, and (c) impregnating the alkali metalenriched zeolite support with a transition metal and a halogen toproduce the supported catalyst. Typically, the alkali metal may comprisepotassium, rubidium, cesium, or combinations thereof, and the transitionmetal may comprise platinum.

Supported catalysts produced by the methods provided herein may be usedin aromatization processes to produce aromatic compounds fromnon-aromatic hydrocarbons. Such catalysts may have the unexpectedcombination of increased product selectivity (e.g., to benzene ortoluene), but with lower catalyst surface area and lower catalystmicropore volume, as compared to supported catalysts prepared without awashing step that utilizes an alkali metal.

Both the foregoing summary and the following detailed descriptionprovide examples and are explanatory only. Accordingly, the foregoingsummary and the following detailed description should not be consideredto be restrictive. Further, features or variations may be provided inaddition to those set forth herein. For example, certain aspects may bedirected to various feature combinations and sub-combinations describedin the detailed description.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 presents a plot of the micropore volume of the alkali metalenriched zeolite support and the micropore volume of the supportedcatalyst versus the molar concentration of the alkali metal in theaqueous solution used to wash the bound zeolite base, for cesium andpotassium alkali metals.

FIG. 2 presents a plot of the platinum dispersion of the supportedcatalyst versus the molar concentration of the alkali metal in theaqueous solution used to wash the bound zeolite base, for cesium andpotassium alkali metals.

FIG. 3 presents a plot of the benzene selectivity, the tolueneselectivity, and the end of run temperature for a cesium-enrichedsupported catalyst compared to a reference catalyst versus the molarconcentration of the cesium in the aqueous solution used to wash thebound zeolite base.

FIG. 4 presents a plot of the benzene selectivity, the tolueneselectivity, and the end of run temperature for a potassium-enrichedsupported catalyst compared to a reference catalyst versus the molarconcentration of the potassium in the aqueous solution used to wash thebound zeolite base.

DEFINITIONS

To define more clearly the terms used herein, the following definitionsare provided. Unless otherwise indicated, the following definitions areapplicable to this disclosure. If a term is used in this disclosure butis not specifically defined herein, the definition from the IUPACCompendium of Chemical Terminology, 2^(nd) Ed (1997), may be applied, aslong as that definition does not conflict with any other disclosure ordefinition applied herein, or render indefinite or non-enabled any claimto which that definition is applied. To the extent that any definitionor usage provided by any document incorporated herein by referenceconflicts with the definition or usage provided herein, the definitionor usage provided herein controls.

Herein, features of the subject matter are described such that, withinparticular aspects, a combination of different features may beenvisioned. For each and every aspect and each and every featuredisclosed herein, all combinations that do not detrimentally affect thedesigns, compositions, processes, or methods described herein arecontemplated with or without explicit description of the particularcombination. Additionally, unless explicitly recited otherwise, anyaspect or feature disclosed herein may be combined to describe inventivedesigns, compositions, processes, or methods consistent with the presentdisclosure.

In this disclosure, while compositions and methods are often describedin terms of “comprising” various components or steps, the compositionsand methods may also “consist essentially of” or “consist of” thevarious components or steps, unless stated otherwise.

The terms “a,” “an,” and “the” are intended to include pluralalternatives, e.g., at least one. For instance, the disclosure of “atransition metal” or “a halogen,” is meant to encompass one, or mixturesor combinations of more than one, transition metal or halogen, unlessotherwise specified.

Generally, groups of elements are indicated using the numbering schemeindicated in the version of the periodic table of elements published inChemical and Engineering News, 63(5), 27, 1985. In some instances, agroup of elements may be indicated using a common name assigned to thegroup; for example, alkali metals for Group 1 elements, transitionmetals for Group 3-12 elements, and halogens or halides for Group 17elements.

For any particular compound or group disclosed herein, any name orstructure (general or specific) presented is intended to encompass allconformational isomers, regioisomers, stereoisomers, and mixturesthereof that may arise from a particular set of substituents, unlessotherwise specified. The name or structure (general or specific) alsoencompasses all enantiomers, diastereomers, and other optical isomers(if there are any) whether in enantiomeric or racemic forms, as well asmixtures of stereoisomers, as would be recognized by a skilled artisan,unless otherwise specified. For example, a general reference to hexaneincludes n-hexane, 2-methyl-pentane, 3-methyl-pentane,2,2-dimethyl-butane, and 2,3-dimethyl-butane; and a general reference toa butyl group includes a n-butyl group, a sec-butyl group, an iso-butylgroup, and a t-butyl group.

In one aspect, a chemical “group” may be defined or described accordingto how that group is formally derived from a reference or “parent”compound, for example, by the number of hydrogen atoms removed from theparent compound to generate the group, even if that group is notliterally synthesized in such a manner. These groups may be utilized assubstituents or coordinated or bonded to metal atoms. By way of example,an “alkyl group” formally may be derived by removing one hydrogen atomfrom an alkane. The disclosure that a substituent, ligand, or otherchemical moiety may constitute a particular “group” implies that thewell-known rules of chemical structure and bonding are followed whenthat group is employed as described. When describing a group as being“derived by,” “derived from,” “formed by,” or “formed from,” such termsare used in a formal sense and are not intended to reflect any specificsynthetic methods or procedures, unless specified otherwise or thecontext requires otherwise.

Various numerical ranges are disclosed herein. When a range of any typeis disclosed or claimed herein, the intent is to disclose or claimindividually each possible number that such a range could reasonablyencompass, including end points of the range as well as any sub-rangesand combinations of sub-ranges encompassed therein, unless otherwisespecified. As a representative example, the present applicationdiscloses that the methods provided herein may employ a molarconcentration of the alkali metal in the aqueous solution in a rangefrom about 0.01 M to about 0.45 M in certain aspects. By a disclosurethat the molar concentration of the alkali metal in the aqueous solutionmay be in a range from about 0.01 M to about 0.45 M, the intent is torecite that the concentration may be any concentration within the rangeand, for example, may be equal to about 0.01 M, about 0.05 M, about 0.1M, about 0.15 M, about 0.2 M, about 0.25 M, about 0.3 M, about 0.35 M,about 0.4 M, or about 0.45 M. Additionally, the molar concentration maybe within any range from about 0.01 M to about 0.45 M (for example, themolar concentration may be in a range from about 0.01 M to about 0.2 M),and this also includes any combination of ranges between about 0.01 Mand about 0.45 M. Likewise, all other ranges disclosed herein should beinterpreted in a manner similar to this example.

The term “about” means that amounts, sizes, formulations, parameters,and other quantities and characteristics are not and need not be exact,but may be approximate including being larger or smaller, as desired,reflecting tolerances, conversion factors, rounding off, measurementerrors, and the like, and other factors known to those of skill in theart. In general, an amount, size, formulation, parameter or otherquantity or characteristic is “about” or “approximate” whether or notexpressly stated to be such. The term “about” also encompasses amountsthat differ due to different equilibrium conditions for a compositionresulting from a particular initial mixture. Whether or not modified bythe term “about,” the claims include equivalents to the quantities. Theterm “about” may mean within 10% of the reported numerical value,preferably within 5% of the reported numerical value.

As used herein, the term “hydrocarbon” refers to a compound containingonly carbon and hydrogen atoms. Other identifiers may be utilized toindicate the presence of particular groups, if any, in the hydrocarbon(e.g., halogenated hydrocarbon indicates the presence of one or morehalogen atoms replacing an equivalent number of hydrogen atoms in thehydrocarbon).

An “aromatic” compound is a compound containing a cyclically conjugateddouble bond system that follows the Hückel (4n+2) rule and contains(4n+2) pi-electrons, where n is an integer from 1 to 5. Aromaticcompounds include “arenes” (hydrocarbon aromatic compounds, e.g.,benzene, toluene, and xylenes) and “heteroarenes” (heteroaromaticcompounds formally derived from arenes by replacement of one or moremethine (—C═) carbon atoms of the cyclically conjugated double bondsystem with a trivalent or divalent heteroatoms, in such a way as tomaintain the continuous pi-electron system characteristic of an aromaticsystem and a number of out-of-plane pi-electrons corresponding to theHückel rule (4n+2)). As disclosed herein, the term “substituted” may beused to describe an aromatic group, arene, or heteroarene, wherein anon-hydrogen moiety formally replaces a hydrogen atom in the compound,and is intended to be non-limiting, unless specified otherwise.

As used herein, the term “alkane” refers to a saturated hydrocarboncompound. Other identifiers may be utilized to indicate the presence ofparticular groups, if any, in the alkane (e.g., halogenated alkaneindicates the presence of one or more halogen atoms replacing anequivalent number of hydrogen atoms in the alkane). The term “alkylgroup” is used herein in accordance with the definition specified byIUPAC: a univalent group formed by removing a hydrogen atom from analkane. The alkane or alkyl group may be linear or branched unlessotherwise specified.

A “cycloalkane” is a saturated cyclic hydrocarbon, with or without sidechains, for example, cyclobutane, cyclopentane, cyclohexane, methylcyclopentane, and methyl cyclohexane. Other identifiers may be utilizedto indicate the presence of particular groups, if any, in thecycloalkane (e.g., halogenated cycloalkane indicates the presence of oneor more halogen atoms replacing an equivalent number of hydrogen atomsin the cycloalkane).

The term “halogen” has its usual meaning. Examples of halogens includefluorine, chlorine, bromine, and iodine.

Molar selectivities are defined as:

$\begin{matrix}{{{Benzene}\mspace{14mu} {selectivity}\text{:}\mspace{14mu} S_{Bz}} = \frac{{\overset{.}{n}}_{{Bz},{prod}}}{{\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 6},{feed}} - {\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 6},{prod}}}} & {{Eq}.\mspace{14mu} 1} \\{{{Toluene}\mspace{14mu} {selectivity}\text{:}\mspace{14mu} S_{Tol}} = \frac{{\overset{.}{n}}_{{Tol},{prod}}}{{\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 7},{feed}} - {\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 7},{prod}}}} & {{Eq}.\mspace{14mu} 2} \\{{{Benzene} + {{Toluene}\mspace{14mu} {selectivity}\text{:}\mspace{14mu} S_{{Bz} + {Tol}}}} = \frac{{\overset{.}{n}}_{{Bz},{prod}} + {\overset{.}{n}}_{{Tol},{prod}}}{{\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 6},{C\; 7},{feed}} - {\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 6},{C\; 7},{prod}}}} & {{Eq}.\mspace{14mu} 3} \\{{{Aromatics}\mspace{14mu} {selectivity}\text{:}\mspace{14mu} S_{arom}} = \frac{{\overset{.}{n}}_{{Bz},{prod}} + {\overset{.}{n}}_{{Tol},{prod}} + {\overset{.}{n}}_{{{C\; 8} + {arom}},{prod}}}{{\overset{.}{n}}_{{{{conv}\mspace{14mu} C\; 6\text{-}C\; 8} +},{feed}} - {\overset{.}{n}}_{{{{conv}\mspace{14mu} C\; 6\text{-}C\; 8} +},{prod}}}} & {{Eq}.\mspace{14mu} 4}\end{matrix}$

Conversion is defined as the number of moles converted per mol of“convertible” components fed:

$\begin{matrix}{{C\; 6\mspace{14mu} {conversion}\text{:}\mspace{14mu} X_{C\; 6}} = \frac{{\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 6},{feed}} - {\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 6},{prod}}}{{\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 6},{feed}}}} & {{Eq}.\mspace{14mu} 5} \\{{C\; 7\mspace{14mu} {conversion}\text{:}\mspace{14mu} X_{C\; 7}} = \frac{{\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 7},{feed}} - {\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 7},{prod}}}{{\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 7},{feed}}}} & {{Eq}.\mspace{14mu} 6} \\{{{C\; 6} + {C\; 7\mspace{14mu} {conversion}\text{:}\mspace{14mu} X_{{C\; 6} + {C\; 7}}}} = \frac{{\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 6},{feed}} + {\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 7},{feed}} - {\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 6},{prod}} - {\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 7},{prod}}}{{\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 6},{feed}} + {\overset{.}{n}}_{{{conv}\mspace{14mu} C\; 7},{feed}}}} & {{Eq}.\mspace{14mu} 7}\end{matrix}$

In these equations, n indicates a molar flow rate in a continuousreactor or the number of moles in a batch reactor.

Although any methods and materials similar or equivalent to thosedescribed herein may be used in the practice or testing of theinvention, the typical methods and materials are herein described.

All publications and patents mentioned herein are incorporated herein byreference for the purpose of describing and disclosing, for example, theconstructs and methodologies that are described in the publications,which might be used in connection with the presently describedinvention.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein are supported catalysts having an enriched alkali metalcontent, methods for producing such catalysts, and the use of thesecatalysts in aromatization or reforming processes.

Methods for Producing Supported Catalysts

Various methods for producing supported catalysts, such as supportedaromatization catalysts, are disclosed and described. One such methodfor producing a supported catalyst may comprise (or consist essentiallyof, or consist of):

(a) providing a bound zeolite base;

(b) washing the bound zeolite base with an aqueous solution comprisingan alkali metal to produce an alkali metal enriched zeolite support; and

(c) impregnating the alkali metal enriched zeolite support with atransition metal and a halogen to produce the supported catalyst.

Generally, the features of any of the methods disclosed herein (e.g.,the zeolite and binder components of the bound zeolite base, thetransition metal, the halogen, the aqueous solution, the alkali metal,the conditions under which the washing step is conducted, and theconditions under which the impregnation step is conducted, among others)are independently described herein, and these features may be combinedin any combination to further describe the disclosed methods. Moreover,other process steps may be conducted before, during, and/or after any ofthe steps listed in the disclosed methods, unless stated otherwise.Additionally, supported catalysts (such as supported aromatizationcatalysts) produced in accordance with any of the disclosedmethods/processes are within the scope of this disclosure and areencompassed herein.

The step in these methods that utilizes an aqueous solution containingan alkali metal often may be referred to as a washing step, while thestep in these methods that utilizes a transition metal and a halogenoften may be referred to as an impregnation step. In the washing step,any compositional attributes of the aqueous solution and the alkalimetal are meant to refer to the incoming aqueous solution and alkalimetal, prior to contacting the bound zeolite base, unless statedotherwise. As one of skill in the art would readily recognize, thecomposition of the aqueous solution after contacting the bound zeolitebase may vary significantly from the composition of the incoming aqueoussolution containing the alkali metal.

Referring now to the bound zeolite base in step (a), any suitable boundzeolite base may be used in the methods of this invention. Typically,the bound zeolite base may comprise an inorganic oxide, examples ofwhich may include, but are not limited to, bound medium and/or largepore zeolites (aluminosilicates), amorphous inorganic oxides, as well asmixtures thereof. Large pore zeolites often may have average porediameters in a range of from about 7 Å to about 12 Å, and non-limitingexamples of large pore zeolites include L-zeolite, Y-zeolite, mordenite,omega zeolite, beta zeolite, and the like. Medium pore zeolites oftenmay have average pore diameters in a range of from about 5 Å to about 7Å. Amorphous inorganic oxides may include, but are not limited to,aluminum oxide, silicon oxide, titania, and combinations thereof.

The term “zeolite” generally refers to a particular group of hydrated,crystalline metal aluminosilicates. These zeolites exhibit a network ofSiO₄ and AlO₄ tetrahedra in which aluminum and silicon atoms arecrosslinked in a three-dimensional framework by sharing oxygen atoms. Inthe framework, the ratio of oxygen atoms to the total of aluminum andsilicon atoms may be equal to 2. The framework exhibits a negativeelectrovalence that typically may be balanced by the inclusion ofcations within the crystal, such as metals, alkali metals, and/orhydrogen.

In some aspects, the bound zeolite base may comprise an L-type zeolite.L-type zeolite supports are a sub-group of zeolitic supports, which maycontain mole ratios of oxides in accordance with the formula: M_(2/n)OA1₂O₃xSiO₂yH₂O. In this formula, “M” designates an exchangeable cation(one or more) such as barium, calcium, cerium, lithium, magnesium,potassium, sodium, strontium, and/or zinc, as well as non-metalliccations like hydronium and ammonium ions, which may be replaced by otherexchangeable cations without causing a substantial alteration of thebasic crystal structure of the L-type zeolite. The “n” in the formularepresents the valence of “M”; “x” is 2 or greater; and “y” is thenumber of water molecules contained in the channels or interconnectedvoids of the zeolite.

In one aspect, the bound zeolite base may comprise a bound potassiumL-type zeolite, also referred to as a K/L-zeolite, while in anotheraspect, the bound zeolite base may comprise a barium ion-exchangedL-zeolite. As used herein, the term “K/L-zeolite” refers to L-typezeolites in which the principal cation M incorporated in the zeolite ispotassium. A K/L-zeolite may be cation-exchanged (e.g., with barium) orimpregnated with a transition metal and one or more halides to produce atransition metal impregnated, halided zeolite or a K/L supportedtransition metal-halide zeolite catalyst.

In the bound zeolite base, the zeolite may be bound with a supportmatrix (or binder), and non-limiting examples of binders may include,but are not limited to, inorganic solid oxides, clays, and the like, aswell as combinations thereof. The zeolite may be bound with the binderor support matrix using any method known in the art. For instance, thebound zeolite base in step (a)—comprising a zeolite and a binder—may beproduced by a process comprising mixing a zeolite, such as aK/L-zeolite, with a binder, such as silica, then extruding the mixture,and then drying and calcining.

In some aspects, the binder may comprise alumina, silica, magnesia,boria, titania, zirconia, or a mixed oxide thereof (e.g., analuminosilicate), or a mixture thereof, while in other aspects, thebinder may comprise a montmorillonite, a kaolin, a cement, or acombination thereof. In a particular aspect contemplated herein, thebinder may comprise silica, alumina, or a mixed oxide thereof;alternatively, silica; alternatively, alumina; or alternatively,silica-alumina. Accordingly, the bound zeolite base may comprise asilica-bound L-zeolite, such as a silica-bound Ba/L-zeolite, or asilica-bound K/L-zeolite.

While not being limited thereto, bound zeolite bases encompassed hereinmay comprise from about 3 wt. % to about 35 wt. % binder. For example,the bound zeolite base may comprise from about 5 wt. % to about 30 wt.%, or from about 10 wt. % to about 30 wt. % binder. These weightpercentages are based on the total weight of the bound zeolite base,excluding transition metal and halogen, for example.

Illustrative examples of bound zeolite bases and their use in supportedcatalysts are described in U.S. Pat. Nos. 5,196,631, 6,190,539,6,406,614, 6,518,470, 6,812,180, and 7,153,801, the disclosures of whichare incorporated herein by reference in their entirety.

Referring now to step (b), also referred to as the washing step, inwhich the bound zeolite base may be washed with any suitable aqueoussolution comprising an alkali metal (or a mixture of alkali metals),resulting in an alkali metal enriched zeolite support. The alkali metalin step (b) may be any Group 1 element. For instance, the alkali metalmay comprise (or consist essentially of, or consist of) potassium,rubidium, or cesium, as well as combinations thereof. In some aspects,the alkali metal may comprise (or consist essentially of, or consist of)potassium; alternatively, rubidium; or alternatively, cesium.

The aqueous solution used in the washing step may contain the alkalimetal (or metals) in any suitable form, but often, the aqueous solutioncontains a salt of the alkali metal. Illustrative salts may include, butare not limited to, chlorides, fluorides, bromides, iodides, nitrates,and the like, as well as combinations thereof. While not wishing to bebound by the following theory, it is believed that nitrates may bedetrimental due to the potential for NOx production during subsequentprocessing. Accordingly, in particular aspects of this invention, theaqueous solution in the washing step may comprise an alkali metal halidesalt, such as potassium chloride, rubidium chloride, or cesium chloride,as well as mixtures thereof.

In addition to water and the alkali metal, the aqueous solution used inthe washing step may contain other components, as would be recognized bythose of skill in the art. However, in some aspects, the washing stepmay comprise contacting the bound zeolite base with an aqueous solutionconsisting essentially of, or consisting of, the alkali metal salt andwater, or the alkali metal salt and deionized water. In these and otheraspects, the aqueous solution used in the washing step (and optionally,any steps in the methods after step (a)) may be substantially free of abasic compound (e.g., a hydroxide), and/or substantially free of ammoniaor any ammonium-containing compounds, and/or substantially free ofsulfur or any sulfur-containing compounds. In these circumstances,“substantially free” is meant to contain less than 100 ppmw (ppm byweight), independently, of any of these materials, and more typically,less than 75 ppmw, less than 50 ppmw, less than 25 ppmw, or less than 10ppmw. Therefore, it is contemplated that the individual amount of any ofthese materials in the aqueous solution (or used in any steps of themethods after step (a)) may be in range from about 0.1 ppmw to 100 ppmw,from about 0.1 ppmw to 75 ppmw, from about 1 ppmw to 100 ppmw, fromabout 1 ppmw to about 75 ppmw, from about 0.1 ppmw to about 50 ppmw,from about 1 ppmw to about 50 ppmw, or from about 1 ppmw to about 25ppmw. While not wishing to be bound by theory, it is believed that itmay be beneficial to have substantially none of these materials presentduring the washing step in the disclosed methods for preparing asupported catalyst, as these materials may adversely affect one or moreof the catalyst activity, catalyst selectivity, catalyst lifetime and/orcatalyst deactivation. Moreover, although not required, the aqueoussolution (and any steps in the methods after step (a)) may besubstantially free of sodium or any sodium-containing compound, i.e.,may contain less than 100 ppmw (ppm by weight) of sodium orsodium-containing compounds. As above, it is contemplated that theamount may be, for instance, less than 75 ppmw, less than 50 ppmw, lessthan 25 ppmw, in a range from about 0.1 ppmw to 100 ppmw, in a rangefrom about 0.1 ppmw to about 75 ppmw, or in a range from about 1 ppmw toabout 75 ppmw, and the like.

Thus, in some aspects, the alkali metal used in the washing step is notsodium, but is one or more of potassium, rubidium, and/or cesium.Additionally or alternatively, step (b) in the disclosed methods may bethe only step in the method of making a supported catalyst that utilizesan alkali metal, for example, an alkali metal salt.

In the washing step, the pH of the aqueous solution is not limited toany particular range. Generally, however, the pH may be in the 6-8range, depending upon the alkali metal salt utilized and its respectiveconcentration.

While not being limited thereto, the amount of the alkali metal in theaqueous solution often may be less than about 5 M (mole/L). Forinstance, the aqueous solution may have a concentration of the alkalimetal of less than about 1 M, less than about 0.75 M, less than about0.5 M, less than about 0.3 M, less than about 0.25 M, or less than about0.2 M. Therefore, suitable ranges for the concentration of the alkalimetal may include, but are not limited to, the following ranges: fromabout 0.01 M to about 5 M, from about 0.01 M to about 1 M, from about0.01 M to about 0.5 M, from about 0.01 M to about 0.45 M, from about0.01 M to about 0.3 M, from about 0.01 M to about 0.25 M, from about0.01 M to about 0.2 M, from about 0.05 M to about 1 M, from about 0.05 Mto about 0.5 M, from about 0.05 M to about 0.45 M, from about 0.05 M toabout 0.3 M, from about 0.05 M to about 0.25 M, or from about 0.05 M toabout 0.2 M, and the like.

Unexpectedly, it was found that lower concentrations of cesium in thewashing step may be beneficial for improved catalyst activity andselectivity. In these aspects, the concentration of the cesium (or thecesium salt) in the aqueous solution may fall within a range from about0.01 M to about 0.25 M, from about 0.01 M to about 0.2 M, from about0.01 M to about 0.15 M, from about 0.025 M to about 0.25 M, from about0.025 M to about 0.2 M, from about 0.025 M to about 0.15 M, from about0.05 M to about 0.25 M, or from about 0.05 M to about 0.2 M.

Also unexpectedly, it was found that slightly higher concentrations ofpotassium in the washing step may be beneficial for improved catalystactivity and selectivity. In these aspects, the concentration of thepotassium (or the potassium salt) in the aqueous solution may fallwithin a range from about 0.1 M to about 0.45 M, from about 0.15 M toabout 0.45 M, from about 0.15 M to about 0.35 M, from about 0.15 M toabout 0.3 M, from about 0.2 M to about 0.45 M, from about 0.2 M to about0.35 M, or from about 0.2 M to about 0.3 M

The washing step containing the alkali metal may be conducted at avariety of temperatures and time periods. For instance, the washing stepmay be conducted at a washing temperature in a range from about 15° C.to about 95° C.; alternatively, from about 15° C. to about 80° C.;alternatively, from about 15° C. to about 70° C.; alternatively, fromabout 15° C. to about 65° C.; alternatively, from about 20° C. to about95° C.; alternatively, from about 20° C. to about 80° C.; alternatively,from about 20° C. to about 70° C.; alternatively, from about 20° C. toabout 50° C.; alternatively, from about 30° C. to about 80° C.;alternatively, from about 30° C. to about 70° C.; alternatively, fromabout 30° C. to about 50° C.; alternatively, from about 25° C. to about55° C.; or alternatively, from about 30° C. to about 45° C. In these andother aspects, these temperature ranges also are meant to encompasscircumstances where the washing step is conducted at a series ofdifferent temperatures, instead of at a single fixed temperature,falling within the respective ranges.

The washing step containing the alkali metal may be conducted byperforming more than one washing cycle containing the alkali metal, suchas from 1 to 4 washing cycles, from 2 to 8 washing cycles, or from 2 to4 washing cycles. Thus, for example, the washing step may comprise from1 to 4 washing cycles, from 2 to 8 washing cycles, or from 2 to 4washing cycles, with each washing cycle, independently, ranging fromabout 1 minute to about 6 hours, from about 5 minutes to about 2 hours,from about 10 minutes to about 45 minutes, or from about 10 minutes toabout 30 minutes, and so forth.

The duration of a single washing cycle containing the alkali metal isnot limited to any particular period of time. Hence, a washing cycle maybe conducted, for example, in a time period ranging from as little as1-5 minutes to as long as 2-4 hours, 6-8 hours, or more. The appropriatewashing cycle time may depend upon, for example, the washingtemperature, the amount of alkali metal in the aqueous solution, and thenumber of washing cycles, among other variables. Generally, however, thewashing cycle step may be conducted in a time period that may be in arange from about 1 minute to about 6 hours, such as, for example, fromabout 1 minute to about 2 hours, from about 5 minutes to about 2 hours,from about 5 minutes to about 1 hour, from about 10 minutes to about 1hour, from about 5 minutes to about 45 minutes, from about 10 minutes toabout 45 minutes, or from about 10 minutes to about 30 minutes.

Generally, the amount of the aqueous solution—containing the alkalimetal—used in the washing step (or in each washing cycle) relative tothe amount of the bound zeolite base is not particularly limited. In oneaspect, for instance, the ratio of the weight of the aqueous solution tothe weight of the bound zeolite base may fall within a range of fromabout 0.4:1 to about 50:1, or from about 0.5:1 to about 25:1. In anotheraspect, the ratio of the weight of the aqueous solution to the weight ofthe bound zeolite base may range from about 0.4:1 to about 10:1, or fromabout 0.5:1 to about 10:1. In yet another aspect, the ratio of theweight of the aqueous solution to the weight of the bound zeolite basemay range from about 0.5:1 to about 8:1, or from about 0.5:1 to about5:1. In still another aspect, the ratio of the weight of the aqueoussolution to the weight of the bound zeolite base may range from about1:1 to about 15:1, or from about 1:1 to about 5:1.

The washing step containing the alkali metal may be conducted using anysuitable technique and equipment. For instance, the bound zeolite basemay be placed into a vessel or tank, and then filled with enough of theaqueous solution containing the alkali metal to exceed the level of thebound zeolite base in the vessel or tank. Optionally, agitation may beprovided in the vessel and tank to increase the contact between thebound zeolite base and the alkali metal within the aqueous solution.Alternatively, the bound zeolite base may be placed in a fixed or packedbed arrangement, and the aqueous solution containing the alkali metalmay be contacted with the bound zeolite by flowing the aqueous solutionthrough the bed of the bound zeolite base. As would be recognized bythose of skill in the art, other suitable techniques and equipment maybe employed for the washing step, and such techniques and equipment areencompassed herein.

Although not required, the washing step may be completed by performingone or more washing cycles without an alkali metal, such as from 1 to 4washing cycles. The washing conditions may be the same as thosedescribed herein for washing steps with an alkali metal.

In step (b) of the methods for producing supported catalyst disclosedherein, the bound zeolite base may be washed with an aqueous solutioncomprising an alkali metal to produce an alkali metal “enriched” zeolitesupport. In effect, the washing step may enrich the bound zeolite basewith any suitable or desired amount of alkali metal, wherein the amountof enrichment is the difference in the amount of the alkali metal in thealkali metal enriched zeolite support versus the amount of the alkalimetal in the bound zeolite base. While not being limited thereto, thewashing step may enrich the bound zeolite base with from about 0.03moles to about 1.5 moles of the alkali metal per kg of the bound zeolitebase (or per kg of the alkali metal enriched zeolite support);alternatively, from about 0.03 moles to about 1 mole of the alkali metalper kg of the bound zeolite base (or per kg of the alkali metal enrichedzeolite support); alternatively, from about 0.03 moles to about 0.7moles of the alkali metal per kg of the bound zeolite base (or per kg ofthe alkali metal enriched zeolite support); alternatively, from about0.05 moles to about 1 mole of the alkali metal per kg of the boundzeolite base (or per kg of the alkali metal enriched zeolite support);alternatively, from about 0.1 moles to about 1.2 moles of the alkalimetal per kg of the bound zeolite base (or per kg of the alkali metalenriched zeolite support); alternatively, from about 0.1 moles to about0.9 moles of the alkali metal per kg of the bound zeolite base (or perkg of the alkali metal enriched zeolite support); alternatively, fromabout 0.2 moles to about 0.8 moles of the alkali metal per kg of thebound zeolite base (or per kg of the alkali metal enriched zeolitesupport); or alternatively, from about 0.3 moles to about 0.7 moles ofthe alkali metal per kg of the bound zeolite base (or per kg of thealkali metal enriched zeolite support). As an example, a bound zeolitebase (containing no cesium) may be washed with an aqueous solutioncontaining a cesium salt (in one or more washing cycles conducted at anytemperature, washing time, and relative amount of the aqueous solutiondisclosed herein) to produce a cesium enriched zeolite supportcontaining about 0.5 moles of cesium per kg of the bound zeolite base(or about 0.5 moles of cesium per kg of the cesium enriched zeolitesupport). As another example, a bound zeolite base (such as a boundK/L-zeolite containing about 3 moles of potassium per kg of the boundK/L-zeolite) may be washed with an aqueous solution containing apotassium salt (in one or more washing cycles conducted at anytemperature, washing time, and relative amount of the aqueous solutiondisclosed herein) to produce a potassium enriched zeolite supportcontaining about 3.1 moles of potassium per kg of the bound K/L-zeolite(or about 3.1 moles per kg of the potassium enriched K/L-zeolitesupport).

As those of skill in the art will readily recognize, the alkali metalenrichment due to the incorporation of an alkali metal during thewashing of the bound zeolite base may be accomplished by variouscombinations of conditions that may be used in step (b). Once a desiredlevel of alkali metal enrichment is selected, this result may beachieved by many different combinations of the number of washing cycles,the washing time, the washing temperature, the molar concentration ofthe alkali metal in the aqueous solution, the relative amount of aqueoussolution used based on the weight of the bound zeolite base, and soforth.

In addition to producing an alkali metal enriched zeolite support duringthe washing step, the level of sodium may be reduced, assuming that thebound zeolite base contains sodium and the aqueous solution does not. Inthese circumstances, the resultant alkali metal enriched zeolite supportmay contain less than about 0.35 wt. % sodium, or less than about 0.3wt. % sodium, based on the weight of the alkali metal enriched zeolitesupport. In some aspects, the amount of sodium in the alkali metalenriched zeolite support may range from about 0.03 wt. % to about 0.35wt. %, from about 0.05 wt. % to about 0.3 wt. %, from about 0.01 wt. %to about 0.25 wt. %, or from about 0.03 wt. % to about 0.2 wt. % sodium,based on the total weight of the zeolite support.

Once the alkali metal enriched zeolite support has been produced in step(b), optionally, the alkali metal enriched zeolite support may be driedand/or calcined prior to step (c). If both drying and calcining areperformed, typically the alkali metal enriched zeolite support is driedand then calcined.

If a drying step is performed, the drying step usually involvescontacting the alkali metal enriched zeolite support with a drying gasstream comprising (or consisting essentially, or consisting of) an inertgas (e.g., nitrogen), oxygen, air, or any mixture or combinationthereof; alternatively, nitrogen; alternatively, helium; alternatively,neon; alternatively, argon; alternatively, oxygen; or alternatively,air. While not being limited thereto, the drying step generally may beconducted at a drying temperature in a range from about 80° C. to about200° C.; alternatively, from about 100° C. to about 200° C.;alternatively, from about 85° C. to about 175° C.; or alternatively,from about 100° C. to about 150° C. In these and other aspects, thesetemperature ranges also are meant to encompass circumstances where thedrying step is conducted at a series of different temperatures, insteadof at a single fixed temperature, falling within the respective ranges.

The duration of the drying step is not limited to any particular periodof time. Typically, the drying step may be conducted in a time periodranging from as little as 30 minutes to as long as 8 hours (or more),but more typically, the drying step may be conducted in a time periodthat may be in a range from about 1 hour to about 8 hours, such as, forexample, from about 1 hour to about 7 hours, from about 1 hour to about6 hours, from about 2 hours to about 7 hours, or from about 2 hours toabout 6 hours.

If a calcining step is performed, the calcining step may be conducted ata variety of temperatures and time periods. Typical peak calciningtemperatures often fall within a range from about 315° C. to about 600°C., such as from about 375° C. to about 600° C., from about 400° C. toabout 550° C., or from about 425° C. to about 500° C. In these and otheraspects, these temperature ranges also are meant to encompasscircumstances where the calcination step is conducted at a series ofdifferent temperatures (e.g., an initial calcination temperature, a peakcalcination temperature), instead of at a single fixed temperature,falling within the respective ranges. For instance, the calcination stepmay start at an initial temperature which is the same as the dryingtemperature in the drying step. Subsequently, the temperature of thecalcination may be increased over time to a peak calcining temperature,for example, in a range from about 375° C. to about 600° C.

The duration of the calcining step is not limited to any particularperiod of time. Hence, the calcining step may be conducted, for example,in a time period ranging from as little as 30-45 minutes to as long as10-12 hours, or more. The appropriate calcining time may depend upon,for example, the initial/peak calcining temperature and whether a dryingstep is used, among other variables. Generally, however, the calciningstep may be conducted in a time period that may be in a range from about45 minutes to about 12 hours, such as, for example, from about 1 hour toabout 12 hours, from about 1 hour to about 10 hours, from about 1 hourto about 5 hours, or from about 1 hour to about 3 hours.

The calcining step may be conducted in a calcining gas stream thatcomprises (or consists essentially of, or consists of) an inert gas(e.g., nitrogen), oxygen, air, or any mixture or combination thereof. Insome aspects, the calcining gas stream may comprise air, while in otheraspects, the calcining gas stream may comprise a mixture of air andnitrogen. Yet, in certain aspects, the calcining gas stream may be aninert gas, such as nitrogen and/or argon.

Referring now to step (c) of the method for producing a supportedcatalyst, the alkali metal enriched zeolite support may be impregnatedwith a transition metal and a halogen to produce the supported catalyst.Non-limiting examples of suitable transition metals may include iron,cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium,platinum, gold, silver, copper, and the like, or a combination of two ormore transition metals. In one aspect, the transition metal may comprisea Group 8-11 transition metal or a Group 8-10 transition metal (one ormore), while in another aspect, the transition metal may compriseplatinum (Pt). In yet another aspect, the alkali metal enriched zeolitesupport is impregnated with only one transition metal, and thetransition metal is platinum.

The transition metal may be added to the zeolitic support by anysuitable method or technique known to those of skill in the art thatresults in adequate dispersion of the transition metal on the support.One such method involves mixing the alkali metal enriched zeolitesupport with a transition metal-containing compound, where thetransition-metal containing compound may be present in a solution of anysuitable solvent, such as water. Illustrative and non-limiting examplesof transition metal-containing compounds that are suitable for use inimpregnating the zeolitic support with platinum include, but are notlimited to, tetraamineplatinum (II) chloride, tetraamineplatinum (II)nitrate, platinum (II) acetyl acetonate, platinum (II) chloride,ammonium tetrachloroplatinate (II), chloroplatinic acid, platinum (II)nitrate, and the like, as well as mixtures or combinations thereof.

In one aspect, the supported catalyst may comprise from about 0.1 wt. %to about 10 wt. % transition metal. In another aspect, the supportedcatalyst may comprise from about 0.2 wt. % to about 5 wt. % transitionmetal. In yet another aspect, the supported catalyst may comprise fromabout 0.3 wt. % to about 3 wt. % transition metal, or from about 0.3 wt.% to about 2 wt. % transition metal. These weight percentages are basedon the total weight of the supported catalyst.

In circumstances where the transition metal comprises platinum, thesupported catalyst may comprise from about 0.1 wt. % to about 10 wt. %platinum; alternatively, from about 0.2 wt. % to about 5 wt. % platinum;alternatively, from about 0.3 wt. % to about 3 wt. % platinum; oralternatively, from about 0.3 wt. % to about 2 wt. % platinum. In aparticular aspect contemplated herein, the supported catalyst maycomprise platinum on a bound K/L-zeolite that has been enriched with analkali metal.

In addition to impregnating the alkali metal enriched zeolite supportwith a transition metal, such as platinum, the alkali metal enrichedzeolite support may be impregnated with a halogen to produce thesupported catalyst. Typically, the halogen comprises chlorine and/orfluorine. Thus, chlorine or fluorine may be utilized singly, or bothchlorine and fluorine may be used. The halogen (one or more) may beadded to the zeolitic support before, during and/or after the additionof the transition metal.

The halogen(s) may be added to the zeolitic support by any suitablemethod or technique known to those of skill in the art. One such methodinvolves contacting or mixing the alkali metal enriched zeolite supportwith a chlorine-containing compound and/or a fluorine-containingcompound, and in any order or sequence. In one aspect, the alkali metalenriched zeolite support may be mixed with a solution of thechlorine-containing compound and/or fluorine-containing compound in anysuitable solvent. Illustrative and non-limiting examples ofchlorine-containing compounds include hydrochloric acid, carbontetrachloride, tetrachloroethylene, chlorobenzene, methyl chloride,methylene chloride, chloroform, allyl chloride, trichloroethylene, achloramine, a chlorine oxide, a chlorine acid, chlorine dioxide,dichlorine monoxide, dichlorine heptoxide, chloric acid, perchloricacid, ammonium chloride, tetramethylammonium chloride, tetraethylammonium chloride, tetrapropylammonium chloride, tetrabutylammoniumchloride, methyltriethylammonium chloride, and the like, as well ascombinations thereof. Illustrative and non-limiting examples offluorine-containing compounds include hydrofluoric acid,2,2,2-trifluoroethanol, tetrafluoroethylene, carbon tetrafluoride,carbon trifluoride, fluoromethane, heptafluoropropane, decafluorobutane,hexafluoroisopropanol, tetrafluoropropanol, pentafluoropropanol,hexafluorophenylpropanol, perfluorobutyl alcohol, hexafluor-2-propanol,pentafluoro-1-propanol, tetrafluoro-1-propanol,1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol,ammonium fluoride, tetramethylammonium fluoride, tetraethyl ammoniumfluoride, tetrapropylammonium fluoride, tetrabutylammonium fluoride,methyltriethylammonium fluoride, and the like, as well as combinationsthereof.

In another aspect, the alkali metal enriched zeolite support may beimpregnated with the halogen(s) in the vapor phase. For instance, thezeolitic support may be contacted with a chlorine-containing streamcomprising a chlorine-containing compound and/or a fluorine-containingstream comprising a fluorine-containing compound, and in any order orsequence. Suitable chlorine-containing compounds and fluorine-containingcompounds include those listed hereinabove, as well as chlorine gas(Cl₂) and fluorine gas (F₂).

When present, the amount of chlorine (Cl), based on the total weight ofthe supported catalyst, often falls within a range from about 0.05 wt. %to about 5 wt. %, from about 0.1 wt. % to about 1.5 wt. %, from about0.2 wt. % to about 1 wt. %, or from about 0.5 wt. % to about 1.5 wt. %chlorine. Likewise, when present, the amount of fluorine (F), based onthe total weight of the supported catalyst, often falls within a rangefrom about 0.05 wt. % to about 5 wt. %, from about 0.1 wt. % to about1.5 wt. %, from about 0.2 wt. % to about 1 wt. %, or from about 0.5 wt.% to about 1.5 wt. % fluorine.

Once the supported catalyst has been produced in step (c), optionally,the supported catalyst may be dried and/or calcined. If both drying andcalcining are performed, typically the supported catalyst is dried andthen calcined. Any suitable temperatures, pressures, durations, andatmospheres may be used in the drying and calcining steps. In someaspects, the step of drying the supported catalyst may be performedsimilarly to the step of drying the alkali metal enriched zeolitesupport described hereinabove (e.g., temperature ranges, ranges oftimes, inert or oxidizing atmospheres, and so forth). In some aspects,the drying step may be performed at any suitable sub-atmosphericpressure, such as less than 125 torr, less than 100 torr, or less than50 torr.

The supported catalyst in step (c) may be calcined. If a calcining stepis performed, the calcining step may be conducted at a variety oftemperatures and time periods. Typical peak calcining temperatures oftenfall within a range from about 175° C. to about 450° C., such as fromabout 200° C. to about 400° C., from about 225° C. to about 350° C., orfrom about 250° C. to about 300° C. In these and other aspects, thesetemperature ranges also are meant to encompass circumstances where thecalcination step is conducted at a series of different temperatures(e.g., an initial calcination temperature, a peak calcinationtemperature), instead of at a single fixed temperature, falling withinthe respective ranges. For instance, the calcination step may start atan initial temperature which is the same as the drying temperature inthe drying step. Subsequently, the temperature of the calcination may beincreased over time to a peak calcining temperature, for example, in arange from about 375° C. to about 600° C.

The duration of the calcining step is not limited to any particularperiod of time. Hence, the calcining step may be conducted, for example,in a time period ranging from as little as 30-45 minutes to as long as10-12 hours, or more. The appropriate calcining time may depend upon,for example, the initial/peak calcining temperature and whether a dryingstep is used, among other variables. Generally, however, the calciningstep may be conducted in a time period that may be in a range from about45 minutes to about 12 hours, such as, for example, from about 1 hour toabout 12 hours, from about 1 hour to about 10 hours, from about 1 hourto about 5 hours, or from about 1 hour to about 3 hours.

The calcining step may be conducted in a calcining gas stream thatcomprises (or consists essentially of, or consists of) an inert gas(e.g., nitrogen), oxygen, air, or any mixture or combination thereof. Insome aspects, the calcining gas stream may comprise air, while in otheraspects, the calcining gas stream may comprise a mixture of air andnitrogen. Yet, in certain aspects, the calcining gas stream may be aninert gas, such as nitrogen and/or argon.

The methods for preparing a supported catalyst disclosed herein mayfurther comprise a reducing step after step (c). This reducing step maycomprise contacting the supported catalyst with a reducing gas streamcomprising hydrogen. Often, the reducing gas stream comprises molecularhydrogen, either alone or with an inert gas, such as helium, neon,argon, nitrogen, and the like, and this includes combinations of two ormore of these inert gasses. In certain aspects, the reducing gas streammay comprise (or consist essentially of, or consist of) molecularhydrogen and nitrogen. Moreover, molecular hydrogen may be the majorcomponent of the reducing gas stream (greater than 50 mol %), while inother aspects, molecular hydrogen may be a minor component (between 5-35mol %).

The reducing step may be conducted at a variety of temperatures and timeperiods. For instance, the reducing step may be conducted at a reducingtemperature in a range from about 100° C. to about 700° C.;alternatively, from about 200° C. to about 600° C.; alternatively, fromabout 200° C. to about 575° C.; alternatively, from about 350° C. toabout 575° C.; alternatively, from about 400° C. to about 550° C.; oralternatively, from about 450° C. to about 550° C. In these and otheraspects, these temperature ranges also are meant to encompasscircumstances where the reducing step is conducted at a series ofdifferent temperatures, instead of at a single fixed temperature,falling within the respective ranges.

The duration of the reducing step is not limited to any particularperiod of time. Hence, the reducing step may be conducted, for example,in a time period ranging from as little as 1 hour to as long as 48-72hours, or more. For example, the reducing step may be conducted in atime period that may be in a range from about 2 hours to about 48 hours,from about 3 hours to about 36 hours, from about 5 hours to about 36hours, from about 2 hours to about 30 hours, or from about 10 hours toabout 30 hours.

In some aspects, the supported catalyst may contain from about 0.05moles to about 1.5 moles of the alkali metal per kg of the supportedcatalyst, while in other aspects, the supported catalyst may containfrom about 0.05 moles to about 1 mole of the alkali metal per kg of thesupported catalyst. For instance, the supported catalyst may containfrom about 0.05 moles to about 0.7 moles of the alkali metal, from about0.1 moles to about 0.9 moles of the alkali metal, from about 0.2 molesto about 0.8 moles of the alkali metal, or from about 0.3 moles to about0.7 moles of the alkali metal, per kg of the supported catalyst. Inthese and other aspects, the supported catalyst may contain from about10,000 ppm to about 125,000 ppm (by weight; from about 1 wt. % to about12.5 wt. %) of the alkali metal, such as from about 20,000 ppm to about100,000 ppm of the alkali metal, from about 25,000 ppm to about 110,000ppm of the alkali metal, from about 30,000 ppm to about 90,000 ppm ofthe alkali metal, or from about 40,000 ppm to about 85,000 ppm of thealkali metal, based on the total weight of the supported catalyst.

The supported catalysts produced in accordance with this invention mayhave a surface area less than that of a catalyst obtained by washing thebound zeolite base with an aqueous solution that does not contain analkali metal, under the same catalyst preparation conditions.Illustrative and non-limiting examples of suitable ranges for thesurface area of the supported catalyst include from about 100 m²/g toabout 170 m²/g, from about 100 m²/g to about 150 m²/g, from about 105m²/g to about 170 m²/g, or from about 105 m²/g to about 160 m²/g.Likewise, illustrative and non-limiting examples of suitable ranges forthe surface area of the alkali metal enriched zeolite support includefrom about 120 m²/g to about 250 m²/g, from about 130 m²/g to about 230m²/g, from about 150 m²/g to about 240 m²/g, or from about 160 m²/g toabout 220 m²/g.

In similar fashion, the supported catalysts produced in accordance withthis invention may have a micropore volume less than that of a catalystobtained by washing the bound zeolite base with an aqueous solution thatdoes not contain an alkali metal, under the same catalyst preparationconditions. Illustrative and non-limiting examples of suitable rangesfor the micropore volume of the supported catalyst may include fromabout 0.015 cc/g to about 0.05 cc/g, from about 0.02 cc/g to about 0.045cc/g, from about 0.025 cc/g to about 0.045 cc/g, or from about 0.0265cc/g to about 0.045 cc/g. Likewise, illustrative and non-limitingexamples of suitable ranges for the micropore volume of the alkali metalenriched zeolite support include from about 0.025 cc/g to about 0.08cc/g, from about 0.03 cc/g to about 0.07 cc/g, from about 0.04 cc/g toabout 0.08 cc/g, or from about 0.045 cc/g to about 0.075 cc/g.

Beneficially, the alkali metal enriched supported catalysts disclosedherein may have excellent platinum dispersion, despite the reducedsurface area and micropore volume. Often, the platinum dispersion fallswithin a range from about 50% to about 70%, from about 52% to about 62%,from about 55% to about 70%, from about 55% to about 65%, or from about55% to about 60%.

Reforming Processes with Aromatization Catalysts

Also encompassed herein are various processes for reforminghydrocarbons. One such reforming process may comprise (or consistessentially of, or consist of) contacting a hydrocarbon feed with asupported aromatization catalyst under reforming conditions in a reactorsystem to produce an aromatic product. The supported aromatizationcatalyst used in the reforming process may be any supported catalystdisclosed herein and/or may be produced by any method for producing asupported catalyst disclosed herein.

The reactor systems for reforming and the respective reformingconditions are well known to those of skill in the art and aredescribed, for example, in U.S. Pat. Nos. 4,456,527, 5,389,235,5,401,386, 5,401,365, 6,207,042, and 7,932,425, the disclosures of whichare incorporated herein by reference in their entirety.

Likewise, typical hydrocarbon feeds are disclosed in these references.Often, the hydrocarbon feed may be a naptha stream or light napthastream. In certain aspects, the hydrocarbon feed may comprisenon-aromatic hydrocarbons, for example, the hydrocarbon feed maycomprise C₆-C₉ alkanes and/or cycloalkanes, or C₆-C₈ alkanes and/orcycloalkanes (e.g., hexane, heptane, cyclohexane), and the like.

The supported catalyst disclosed herein may be characterized by aT_(EOR) (end of run temperature) as described herein, which often mayfall within a range from about 499° C. (930° F.) to about 530° C. (986°F.), from about 499° C. (930° F.) to about 524° C. (975° F.), from about499° C. (930° F.) to about 515° C. (959° F.), or from about 501° C.(934° F.) to about 521° C. (970° F.).

Despite the reduced surface area and pore volume of the alkali metalenriched supported catalysts, these catalysts—in addition to anaromatics yield, quantified by the T_(EOR), that is comparable tosupported catalysts without the alkali metal enrichment—also may haveunexpected improvements in selectivity. For instance, the supportedcatalysts disclosed herein may have a benzene selectivity (or a tolueneselectivity) greater than that of a catalyst obtained by washing thebound zeolite base with an aqueous solution that does not contain analkali metal, under the same catalyst preparation and aromatizationreaction conditions. Such catalyst selectivity comparisons are meant tohave the same amount of platinum and halogen on the catalyst, use thesame bound zeolite base, tested on the same equipment and under the sametest method and conditions, and so forth, such that the only differenceis the use of the alkali metal (or not) during the washing step.

While not being limited thereto, typical benzene selectivities (andtoluene selectivities) often may fall within a range from about 0.91 toabout 0.97, from about 0.92 to about 0.98, from about 0.92 to about0.97, from about 0.94 to about 0.98, from about 0.95 to about 0.98, fromabout 0.95 to about 0.975, or from about 0.95 to about 0.97, asdetermined using the testing procedure and conditions described herein.

EXAMPLES

The invention is further illustrated by the following examples, whichare not to be construed in any way as imposing limitations to the scopeof this invention. Various other aspects, modifications, and equivalentsthereof which, after reading the description herein, may suggestthemselves to one of ordinary skill in the art without departing fromthe spirit of the present invention or the scope of the appended claims.

Supported catalysts were tested for their performance in aromatizationreactions using the following general procedure. The supportedaromatization catalysts were ground and sieved to about 25-45 mesh, and1 cc of the sieved catalyst was placed in a ⅜-inch OD stainless steelreactor vessel in a temperature controlled furnace. After reducing thecatalyst under flowing molecular hydrogen, a feed stream of aliphatichydrocarbons and molecular hydrogen was introduced to the reactor vesselat a pressure of 100 psig, a H₂:hydrocarbon molar ratio of 1.3, and aliquid hourly space velocity (LHSV) of 12 hr⁻¹ to obtain catalystperformance data over time. The aliphatic hydrocarbon feed containedapproximately 0.61 mole fraction of convertible C₆ species and 0.21 molefraction of convertible C₇ species. The balance was aromatics, C₈+, andhighly branched isomers, which are classified as nonconvertibles. Thereactor effluent composition was analyzed by gas chromatography todetermine the amounts of the numerous feedstock components and productcomponents, including benzene and toluene present (for selectivitycalculations).

Catalyst performance was quantified by the temperature needed to obtainan aromatics yield of 63 wt. %. The T_(EOR) (end of run temperature) isthe temperature giving the desired yield at the end of the run, whichwas approximately 40 hours.

Alkali metal content (moles of alkali metals) of the alkali metalenriched zeolite support was determined by XRF or ICP. Weightpercentages of Pt, Cl, and F were determined using X-ray fluorescence(XRF). Surface areas were determined using the BET method, and microporevolumes were determined using the t-plot method. Platinum dispersion wasdetermined by CO Chemisorption.

Examples 1-5

A standard bound KL-zeolite consisting of approximately 17 wt. % silicabinder was used as the starting material for Examples 1-5. The boundzeolite base was washed either with water (Example 1) or with watercontaining 0.1 M of an alkali metal salt (NaCl, KCl, RbCl, orCsCl—Examples 2-5). The washing conditions consisted of 3 wash cycles,each conducted at 100° F. for 20 minutes with the weight of the washwater (with or without alkali metal) being 2.5 times the weight of thebound zeolite base. The washing was performed batchwise with N₂ bubblingto agitate the mixture.

Table I summarizes the metals analysis of the alkali metal enrichedzeolite supports after drying and calcining in air at 250° F. and 900°F., respectively. The alkali metal washing steps with rubidium or cesium(Examples 4-5) significantly reduced the amount of sodium in thesupport, and resulted in about 0.5 moles of the respective alkali metal(per kg) in the alkali metal enriched zeolite support. Alkali washingwith potassium also reduced the amount of sodium in the support. Asshown by Examples 4-5, alkali washing with rubidium or cesium alsoreduced the potassium content of the support.

The alkali metal enriched zeolite supports were subsequently impregnatedwith platinum and halogen, dried (at 95° C.), and calcined (at 900° F.)to form the supported aromatization catalysts. Pt, Cl, and F were addedin one step via incipient wetness techniques. Final Pt, Cl, and Floadings were all approximately 1 wt. %. Table II summarizes themicropore volumes and surface areas of the alkali metal enriched zeolitesupports and the supported catalysts after drying/calcining, as well asthe platinum dispersion of the supported catalysts. In Table II,“support” is the alkali metal enriched zeolite support prior to platinumand halogen addition, and “catalyst” is the final supported catalystcontaining platinum and halogen. Generally, the alkali metal washingsteps with KCl, RbCl, or CsCl (Examples 3-5) reduced the surface areaand the micropore volume of the alkali metal enriched zeolite supportand the supported catalyst, with the cesium-enriched support andcesium-enriched catalyst having the lowest micropore volumes and surfaceareas. However, despite the impact of the alkali metal washing step onthe micropore volume and surface area, the dispersion of the platinum onthe supported catalyst was similar for each of Examples 1-5.

Additional experiments were conducted with potassium and cesium, similarto Example 3 and Example 5, respectively, in which the molarconcentration of the alkali metal in the wash water was varied from 0.05M to 0.3 M. FIG. 1 illustrates the impact of the molar concentration ofpotassium and cesium in the aqueous solution used to wash the boundzeolite base on the micropore volumes of the alkali metal enrichedzeolite supports and the supported catalysts. Generally, as alkali metalconcentration increased, the micropore volume decreased, although thedecrease was not as significant for the supported catalyst as comparedto that of the alkali metal enriched zeolite support.

For the same 0.05 M to 0.3 M range of alkali metal concentration in thewash water, FIG. 2 illustrates the impact of the alkali metalconcentration on the platinum dispersion on the supported catalyst.Unexpectedly, the platinum dispersion when using potassium wasrelatively unaffected throughout the concentration range, while whenusing cesium, the platinum dispersion dropped significantly at higher0.2-0.3 M concentrations.

The supported catalysts of Examples 1-5, as characterized in Table I andTable II, were evaluated in aromatization reactions for their relativeperformance. Unexpectedly, given the reduction in surface area and porevolume for the alkali metal enriched supported catalysts of Examples 3-5(see Table II), the aromatics yields as measured by the T_(EOR) in TableIII were similar for each of Examples 1-5. However, Table IIIdemonstrates that the alkali metal enriched supported catalysts ofExamples 3-5 had an unexpected improvement in benzene selectivity, withcesium enrichment increasing benzene selectivity of the supportedcatalyst to over 96%.

Additional aromatization experiments were conducted with potassium andcesium enriched supported catalysts, similar to Example 3 and Example 5,respectively, in which the molar concentration of the alkali metal inthe wash water was varied from 0.05 M to 0.3 M. FIG. 3 illustrates theimpact of the molar concentration of cesium in the aqueous solution usedto wash the bound zeolite base on the benzene selectivity, tolueneselectivity, and the T_(EOR) of the resultant supported catalysts. Ascompared to a reference (using no alkali metal in the washing step), itwas surprisingly found that cesium concentrations of less than 0.2 Mprovided the beneficial combination of increased benzene selectivity,increased toluene selectivity, and a similar temperature needed(T_(EOR)) to obtain the desired aromatics yield.

Likewise, FIG. 4 illustrates the impact of the molar concentration ofpotassium in the aqueous solution used to wash the bound zeolite base onthe benzene selectivity, toluene selectivity, and the T_(EOR) of theresultant supported catalysts. As compared to a reference (using noalkali metal in the washing step), it was surprisingly found thatpotassium concentrations of 0.1 M and above provided the beneficialcombination of increased benzene selectivity, increased tolueneselectivity, and a similar temperature needed (T_(EOR)) to obtain thedesired aromatics yield (no impact on temperature was evident).

TABLE I Examples 1-5 - Alkali metal content. Alkali Total Metal MolesMoles Moles Moles moles Wash Na K Rb Cs cation Example Salt per kg perkg per kg per kg per kg 1 None 0.145 2.93 0 0 3.08 2 NaCl 0.349 2.76 0 03.11 3 KCl 0.052 2.98 0 0 3.03 4 RbCl 0.052 2.41 0.525 0 2.99 5 CsCl0.046 2.15 0 0.545 2.74

TABLE II Examples 1-5 - Micropore volume, surface area, and platinumdispersion. Support Catalyst Alkali Micro- Support Micro- Catalyst Metalpore Surface pore Surface Wash Volume Area Volume Area Platinum ExampleSalt (cc/g) (m²/g) (cc/g) (m²/g) Dispersion 1 None 0.095 265 0.0530 17864.5 2 NaCl 0.078 231 0.0485 167 61.8 3 KCl 0.066 205 0.0363 132 56.7 4RbCl 0.063 195 0.0409 143 59.5 5 CsCl 0.061 191 0.0315 119 58.8

TABLE III Examples 1-5 - Catalyst performance summary. Example Wash SaltBenzene Selectivity T_(EOR) (° F.) 1 None 0.942 942 2 NaCl 0.938 946 3KCl 0.955 943 4 RbCl 0.953 937 5 CsCl 0.962 947

The invention is described above with reference to numerous aspects andspecific examples. Many variations will suggest themselves to thoseskilled in the art in light of the above detailed description. All suchobvious variations are within the full intended scope of the appendedclaims. Other aspects of the invention may include, but are not limitedto, the following (aspects are described as “comprising” but,alternatively, may “consist essentially of” or “consist of”):

Aspect 1. A method of producing a supported catalyst, the methodcomprising:

(a) providing a bound zeolite base;

(b) washing the bound zeolite base with an aqueous solution comprisingan alkali metal to produce an alkali metal enriched zeolite support; and

(c) impregnating the alkali metal enriched zeolite support with atransition metal and a halogen to produce the supported catalyst.

Aspect 2. The method defined in aspect 1, wherein the alkali metalcomprises potassium, rubidium, cesium, or combinations thereof.

Aspect 3. The method defined in aspect 1 or 2, wherein the aqueoussolution comprises an alkali metal salt.

Aspect 4. The method defined in any one of the preceding aspects,wherein the aqueous solution comprises an alkali metal chloride salt.

Aspect 5. The method defined in any one of aspects 1-4, wherein thealkali metal comprises potassium.

Aspect 6. The method defined in any one of aspects 1-4, wherein thealkali metal comprises rubidium.

Aspect 7. The method defined in any one of aspects 1-4, wherein thealkali metal comprises cesium.

Aspect 8. The method defined in any of the preceding aspects, whereinthe bound zeolite base comprises a zeolite and a binder.

Aspect 9. The method defined in aspect 8, wherein the bound zeolite basecomprises any weight percentage of binder disclosed herein, e.g., fromabout 3 wt. % to about 35 wt. %, or from about 5 wt. % to about 30 wt. %binder, based on the total weight of the bound zeolite base.

Aspect 10. The method defined in aspect 8 or 9, wherein the bindercomprises an inorganic solid oxide, a clay, or a combination thereof.

Aspect 11. The method defined in aspect 8 or 9, wherein the bindercomprises alumina, silica, magnesia, boria, titania, zirconia, a mixedoxide thereof, or a mixture thereof.

Aspect 12. The method defined in aspect 8 or 9, wherein the bindercomprises silica.

Aspect 13. The method defined in aspect 8 or 9, wherein the bindercomprises montmorillonite, kaolin, cement, or a combination thereof.

Aspect 14. The method defined in any one of the preceding aspects,wherein the bound zeolite base comprises a bound L-zeolite.

Aspect 15. The method defined in any one of aspects 1-13, wherein thebound zeolite base comprises a bound Ba/L-zeolite.

Aspect 16. The method defined in any one of aspects 1-13, wherein thebound zeolite base comprises a bound K/L-zeolite.

Aspect 17. The method defined in any one of aspects 1-12, wherein thebound zeolite base comprises a silica-bound K/L-zeolite

Aspect 18. The method defined in any one of the preceding aspects,wherein the bound zeolite base in step (a) is produced by a processcomprising mixing a zeolite with a binder, extruding the mixture,drying, and calcining.

Aspect 19. The method defined in any one of aspects 1-12, wherein thebound zeolite base in step (a) is produced by a process comprisingmixing a K/L-zeolite with silica, extruding the mixture, drying, andcalcining.

Aspect 20. The method defined in any one of the preceding aspects,wherein the washing step comprises contacting the bound zeolite basewith any aqueous solution disclosed herein, e.g., consisting essentiallyof, or consisting of, an alkali metal salt and water, or an alkali metalsalt and deionized water.

Aspect 21. The method defined in any one of the preceding aspects,wherein the washing step is conducted at any washing temperaturedisclosed herein, e.g., in a range from about 20° C. to about 95° C.,from about 15° C. to about 65° C., or from about 30° C. to about 50° C.

Aspect 22. The method defined in any one of the preceding aspects,wherein the washing step includes any number of washing cycles (e.g.,from 1 to 4, or from 2 to 8) and any washing cycle time periodsdisclosed herein (e.g., in a range of from about 1 minute to about 6hours, or from about 5 minutes to about 2 hours).

Aspect 23. The method defined in any one of the preceding aspects,wherein the concentration of the alkali metal in the aqueous solution isin any concentration range disclosed herein, e.g., from about 0.01 M toabout 5 M, from about 0.01 M to about 1 M, from about 0.01 M to about0.45 M, or from about 0.05 M to about 0.3 M.

Aspect 24. The method defined in any one of the preceding aspects,wherein the ratio of the weight of the aqueous solution to the weight ofthe bound zeolite base is in any range of weight ratios disclosedherein, e.g., from about 0.4:1 to about 10:1, from about 0.5:1 to about8:1, or from about 1:1 to about 5:1.

Aspect 25. The method defined in any one of the preceding aspects,wherein the washing step enriches the bound zeolite base with any molaramount of alkali metal disclosed herein, e.g., from about 0.03 moles toabout 1 mole, from about 0.1 moles to about 0.9 moles, or from about0.03 moles to about 0.7 moles, of alkali metal per kg of the boundzeolite base (or per kg of the alkali metal enriched zeolite support).

Aspect 26. The method defined in any one of the preceding aspects,wherein the alkali metal enriched zeolite support comprises any weightpercentage of sodium disclosed herein, e.g., from 0 wt. % to about 0.35wt. %, from 0 wt. % to about 0.3 wt. %, from about 0.03 wt. % to about0.35 wt. %, or from about 0.05 wt. % to about 0.3 wt. % sodium, based onthe total weight of the alkali metal enriched zeolite support.

Aspect 27. The method defined in any one of the preceding aspects,wherein step (b) is the only step in the method that utilizes an alkalimetal, for example, an alkali metal salt.

Aspect 28. The method defined in any one of the preceding aspects,wherein the method further comprises drying and/or calcining the alkalimetal enriched zeolite support prior to step (c).

Aspect 29. The method defined in any one of the preceding aspects,wherein the supported catalyst comprises any weight percentage oftransition metal disclosed herein, e.g., from about 0.1 wt. % to about10 wt. %, from about 0.2 wt. % to about 5 wt. %, or from about 0.3 wt. %to about 2 wt. % transition metal, based on the total weight of thesupported catalyst.

Aspect 30. The method defined in any one of the preceding aspects,wherein the transition metal comprises platinum.

Aspect 31. The supported catalyst defined in any one of the precedingaspects, wherein the transition metal is platinum.

Aspect 32. The method defined in any one of the preceding aspects,wherein the supported catalyst comprises any weight percentage range ofplatinum disclosed herein, e.g., from about 0.1 wt. % to about 10 wt. %,from about 0.2 wt. % to about 5 wt. %, or from about 0.3 wt. % to about2 wt. % platinum, based on the total weight of the supported catalyst.

Aspect 33. The method defined in any one of the preceding aspects,wherein step (c) comprises mixing the alkali metal enriched zeolitesupport with a transition metal-containing compound comprisingtetraamineplatinum (II) chloride, tetraamineplatinum (II) nitrate,platinum (II) acetylacetonate, platinum (II) chloride, ammoniumtetrachloroplatinate (II), chloroplatinic acid, platinum (II) nitrate,or a combination thereof.

Aspect 34. The method defined in any one of the preceding aspects,wherein the halogen comprises chlorine and/or fluorine.

Aspect 35. The method defined in any one of the preceding aspects,wherein step (c) comprises mixing the alkali metal enriched zeolitesupport with a chlorine-containing compound and/or a fluorine-containingcompound.

Aspect 36. The method defined in any one of aspects 1-35, wherein thehalogen comprises chlorine.

Aspect 37. The method defined in aspect 36, wherein the supportedcatalyst comprises any weight percentage of chlorine disclosed herein,e.g., from about 0.05 wt. % to about 5 wt. %, from about 0.1 wt. % toabout 1.5 wt. %, from about 0.2 wt. % to about 1 wt. % chlorine, basedon the total weight of the supported catalyst.

Aspect 38. The method defined in any one of aspects 1-37, wherein thehalogen comprises fluorine.

Aspect 39. The method defined in aspect 38, wherein the supportedcatalyst comprises any weight percentage of fluorine disclosed herein,e.g., from about 0.05 wt. % to about 5 wt. %, from about 0.1 wt. % toabout 1.5 wt. %, from about 0.2 wt. % to about 1 wt. % fluorine, basedon the total weight of the supported catalyst.

Aspect 40. The method defined in any one of the preceding aspects,wherein the method further comprises drying and/or calcining thesupported catalyst after step (c).

Aspect 41. The method defined in any one of the preceding aspects,wherein the method further comprises a reducing step after step (c), thereducing step comprising contacting the supported catalyst with anyreducing gas stream disclosed herein, e.g., comprising hydrogen.

Aspect 42. The method defined in aspect 41, wherein the reducing step isconducted at any reducing temperature disclosed herein, e.g., in a rangefrom about 100° C. to about 700° C., or from about 200° C. to about 600°C.

Aspect 43. A supported catalyst obtained by the method defined in anyone of the preceding aspects, e.g., a supported aromatization catalyst.

Aspect 44. The supported catalyst or method defined in any one of thepreceding aspects, wherein the supported catalyst comprises any ppmamount (by weight) of the alkali metal disclosed herein, e.g., fromabout 10,000 ppm to about 125,000 ppm (from about 1 wt. % to about 12.5wt. %), from about 20,000 ppm to about 100,000 ppm (from about 2 wt. %to about 10 wt. %), or from about 30,000 ppm to about 90,000 ppm (fromabout 3 wt. % to about 9 wt. %), based on the total weight of thesupported catalyst.

Aspect 45. The supported catalyst or method defined in any one of thepreceding aspects, wherein the supported catalyst has a surface arealess than that of a catalyst obtained by washing the bound zeolite basewith an aqueous solution that does not contain an alkali metal, underthe same catalyst preparation conditions.

Aspect 46. The supported catalyst or method defined in any one of thepreceding aspects, wherein the supported catalyst has a surface area inany range of surface area disclosed herein, e.g., from about 100 m²/g toabout 170 m²/g, or from about 100 m²/g to about 150 m²/g.

Aspect 47. The supported catalyst or method defined in any one of thepreceding aspects, wherein the alkali metal enriched zeolite support hasa surface area in any range of surface area disclosed herein, e.g., fromabout 120 m²/g to about 250 m²/g, or from about 130 m²/g to about 230m²/g.

Aspect 48. The supported catalyst or method defined in any one of thepreceding aspects, wherein the supported catalyst has a micropore volumearea less than that of a catalyst obtained by washing the bound zeolitebase with an aqueous solution that does not contain an alkali metal,under the same catalyst preparation conditions.

Aspect 49. The supported catalyst or method defined in any one of thepreceding aspects, wherein the supported catalyst has a micropore volumein any range of micropore volume disclosed herein, e.g., from about0.015 cc/g to about 0.05 cc/g, or from about 0.02 cc/g to about 0.045cc/g.

Aspect 50. The supported catalyst or method defined in any one of thepreceding aspects, wherein the alkali metal enriched zeolite support hasa micropore volume in any range of micropore volume disclosed herein,e.g., from about 0.025 cc/g to about 0.08 cc/g, or from about 0.03 cc/gto about 0.07 cc/g.

Aspect 51. The supported catalyst or method defined in any one of thepreceding aspects, wherein the supported catalyst is characterized by aT_(EOR) in any range disclosed herein, e.g., from about 499° C. (930°F.) to about 530° C. (986° F.).

Aspect 52. The supported catalyst or method defined in any one of thepreceding aspects, wherein the supported catalyst is characterized by abenzene selectivity (or a toluene selectivity) in any selectivity rangedisclosed herein, e.g., from about 0.91 to about 0.97, from about 0.92to about 0.98, from about 0.92 to about 0.97, or from about 0.95 toabout 0.98.

Aspect 53. The supported catalyst or method defined in any one of thepreceding aspects, wherein the supported catalyst has a benzeneselectivity (or a toluene selectivity) greater than that of a catalystobtained by washing the bound zeolite base with an aqueous solution thatdoes not contain an alkali metal, under the same catalyst preparationand aromatization reaction conditions.

Aspect 54. The supported catalyst or method defined in any one of thepreceding aspects, wherein the supported catalyst has a platinumdispersion in any range disclosed herein, e.g., from about 50% to about70%, from about 50% to about 65%, or from about 55% to about 70%.

Aspect 55. A reforming process comprising contacting a hydrocarbon feedwith a supported aromatization catalyst under reforming conditions in areactor system to produce an aromatic product, wherein the supportedaromatization catalyst is the supported catalyst defined in any one ofthe preceding aspects.

Aspect 56. The process defined in aspect 55, wherein the hydrocarbonfeed is any hydrocarbon feed disclosed herein, for example, comprisingnon-aromatic hydrocarbons, comprising C₆-C₉ alkanes and/or cycloalkanes,or comprising C₆-C₈ alkanes and/or cycloalkanes.

1. A method of producing a supported catalyst, the method comprising:(a) providing a bound zeolite base; (b) washing the bound zeolite basewith an aqueous solution comprising cesium to produce a cesium enrichedzeolite support; and (c) impregnating the cesium enriched zeolitesupport with a transition metal and a halogen to produce the supportedcatalyst; wherein the concentration of cesium in the aqueous solution isin a range from about 0.01 M to about 5 M.
 2. The method of claim 1,wherein: the bound zeolite base comprises a silica-bound K/L-zeolite;the transition metal comprises platinum; and the halogen compriseschlorine, fluorine, or both.
 3. The method of claim 1, wherein: theaqueous solution further comprises potassium, rubidium, or a combinationthereof; and the supported catalyst comprises from about 5 wt. % toabout 30 wt. % of a binder, based on the total weight of the supportedcatalyst.
 4. The method of claim 1, wherein the supported catalystcomprises: from about 0.2 wt. % to about 5 wt. % transition metal; fromabout 0.2 wt. % to about 3 wt. % halogen; and from about 2 wt. % toabout 10 wt. % cesium; based on the total weight of the supportedcatalyst.
 5. The method of claim 1, wherein step (b) comprises from 2 to8 washing cycles, each washing cycle conducted independently at awashing temperature in a range from about 20° C. to about 95° C. and fora time period in a range from about 5 minutes to about 2 hours.
 6. Themethod of claim 5, wherein a ratio of the weight of the aqueous solutionto the weight of the bound zeolite base in each washing cycleindependently is in a range about 0.4:1 to about 10:1.
 7. The method ofclaim 1, wherein the concentration of cesium in the aqueous solution isin a range from about 0.01 M to about 0.2 M.
 8. The method of claim 1,wherein the cesium enriched zeolite support comprises: from about 0.03wt. % to about 0.35 wt. % sodium, based on the total weight of thecesium enriched zeolite support; and from about 0.1 moles to about 0.9moles of cesium per kg of the cesium enriched zeolite support.
 9. Themethod of claim 1, wherein: the supported catalyst is characterized by abenzene selectivity in a range from about 0.92 to about 0.98; thesupported catalyst has a benzene selectivity greater than that of acatalyst obtained by washing the bound zeolite base with an aqueoussolution that does not contain an alkali metal, under the same catalystpreparation and aromatization reaction conditions; and the supportedcatalyst has a platinum dispersion in a range from about 50% to about65%.
 10. The method of claim 1, further comprising a step of contactinga hydrocarbon feed with the supported catalyst under reformingconditions in a reactor system to produce an aromatic product. 11-21.(canceled)
 22. The method of claim 1, wherein: the transition metalcomprises platinum; the halogen comprises fluorine and chlorine; and thesupported catalyst comprises: from about 2 wt. % to about 10 wt. %cesium; from about 0.2 wt. % to about 5 wt. % platinum; from about 0.1wt. % to about 1.5 wt. % fluorine; and from about 0.1 wt. % to about 1.5wt. % chlorine; based on the total weight of the supported catalyst. 23.The method of claim 22, wherein the bound zeolite base comprises a boundL-zeolite.
 24. The method of claim 23, wherein the supported catalysthas a surface area in a range from about 100 m²/g to about 150 m²/g anda micropore volume in a range from about 0.02 cc/g to about 0.045 cc/g.25. The method of claim 23, wherein the concentration of cesium in theaqueous solution is in a range from about 0.025 M to about 0.25 M. 26.The method of claim 23, wherein the supported catalyst has a platinumdispersion in a range from about 50% to about 70%.
 27. The method ofclaim 1, wherein the cesium enriched zeolite support comprises fromabout 0.1 moles to about 0.9 moles of cesium per kg of the cesiumenriched zeolite support.
 28. The method of claim 27, wherein: the boundzeolite base comprises a silica-bound K/L-zeolite; the transition metalcomprises platinum; and the halogen comprises chlorine, fluorine, orboth.
 29. The method of claim 10, wherein the hydrocarbon feed comprisesC₆-C₈ alkanes and/or cycloalkanes.